Electric discharge lamps

ABSTRACT

In a tubular high pressure electric discharge lamp, for example a high pressure sodium lamp, the conformation of the interior and/or exterior longitudinal surface of the tubular discharge envelope wall is such as to produce a non-circular cross-section of the interior and/or exterior of the envelope, the configuration of the envelope being such as to give an asymmetric polar distribution of the light emitted from the lamp as a whole. The envelope may be of uniform wall thickness, both the exterior and the interior being of similar non-circular cross-section, for example elliptical, ovate or substantially rectangular. Alternatively, the wall may be of varying thickness around the circumference, such that one or more optical elements, for example lenses, prisms or multiple prisms, are incorporated in the wall structure, the internal and external cross-sections of the tube thus being of different shape, and possibly one or the other being circular. The preferred material for the fabrication of the envelope is transparent crystalline corundum.

United States Patent Nelson et al.

Sydney Alfred Richard Rigden, Hemel Hempstead, both of England [73]Assignee: The General Electric Company Limited, London, England [22]Filed: Apr. 9, 1973 [21] Appl. No.: 349,003

[30] Foreign Application Priority Data Apr. 19, 1972 United Kingdom18095/72 [52] US. Cl 313/110; 220/21 R; 313/220; 313/221 [51] Int. ClI101] 5/16; H01 17/16 H01j/61/33 [58] Field ofSearch 313/110, 111, 112,220, 313/221, 284; 220/21 R, 2.2, 2.3

[56] References Cited UNITED STATES PATENTS 1,853,497 5/1932 Hall313/111 2,362,171 11/1944 Swanson 313/110 2,482,421 9/1949 Lemmers 4313/220 X 2,775,718 12/1956 Dubilier 313/220 X 3,119,040 1/1964 Gardineret al..... 313/220 X 3,243,635 3/1966 Louden et al l 313/220 X 3,385,4635/1968 Lange 313/220 UX A l 6 z r I [451 May 20, 1975 2/1969 Rigden eta1 313/284 10/1969 Zollweg et a1. 313/220 Primary Examiner-Alfred L.Brody Attorney, Agent, or Firm-Kirschstein, Kirschstein, Ottinger &Frank [57] ABSTRACT In a tubular high pressure electric discharge lamp,for example a high pressure sodium lamp, the con1ormation of theinterior and/or exterior longitudinal surface of the tubular dischargeenvelope wall is such as to produce a non-circular cross-section of theinterior and/or exterior of the envelope, the configuration of theenvelope being such as to give an asymmetric polar distribution of thelight emitted from the lamp as a whole. The envelope may be of uniformwall thickness, both the exterior and the interior being of similarnon-circular cross-section, for example elliptical, ovate orsubstantially rectangular. Alternatively, the wall may be of varyingthickness around the circumference, such that one or more opticalelements, for example lenses, prisms or multiple prisms, areincorporated in the wall structure, the internal and externalcross-sections of the tube thus being of different shape, and possiblyone or the other being circular The preferred material for thefabrication of the envelope is transparent crystalline corundum.

10 Claims, 17 Drawing Figures ELECTRIC DISCHARGE LAMPS This inventionrelates to high pressure electric discharge lamps of the type comprisinga tubular discharge envelope formed of light-transmissive material witha pair of electrodes disposed coaxially within said envelope and carriedrespectively by closure means closing each end of the envelope.

It is an object of the present invention to provide an improved form ofdischarge envelope for a lamp of this type, whereby the polardistribution of the light emitted by the lamp in operation can becontrolled.

According to the invention, in an electric discharge lamp of the typereferred to, the conformation of the interior and/or exteriorlongitudinal surface of the tu bular discharge envelope wall is such asto produce a non-circular cross-section of the interior and/or exteriorof the envelope, the resulting configuration of the envelope being suchas to give, in operation, an asymmetric polar distribution of the lightemitted from the lamp as a whole.

The envelope may be formed of a light-transmissive materialconventionally used for the construction of the discharge envelopes ofhigh pressure discharge lamps, such as fused silica or sinteredpolycrystalline alumina, but the preferred material is crystallinecorundum, which is transparent and therefore has the obvious advantageof improved light transmissivity in comparison with that of thetranslucent polycrystalline alumina used hitherto especially for thedischarge envelopes of high pressure sodium vapour lamps. Crystallinecorundum is further advantageous for use for forming the envelopes oflamps in accordance with the invention, since it can readily befabricated in the form of tubes of any desired predeterminedcross-sectional size and configuration, by a known crystal growingtechnique comprising pulling from a melt film supported on a tubularmember of appropriate cross section: a tube so produced may bemonocrystalline or may consist of a few large crystals.

The interior and exterior surfaces of the tubular en velope wall may beof parallel conformation, so that the wall thickness is uniform, boththe exterior and the interior of the tube being of similar non-circularcrosssection, for example elliptical, ovate, or substantiallyrectangular, that is to say in the form of a rectangle with curvedcorners necessitated by the nature of the material employed for theconstruction of the tube. Alternatively, where the tube is formed offused silica or crystalline corundum, the wall may be of varyingthickness around the circumference of the tube, one or more opticalelements such as lenses, prisms or multiple prisms being incorporated inthe wall structure, the internal and external cross-sections of the tubethus differing in shape. and possibly one or the other being cir cular.Usually the configuration of the tube will be so designed that themaximum emission of light from the lamp in operation will be obtainedfrom two opposite regions of the cross-section thereof, but if desiredthe maximum emission may be arranged to be derived from adjacent regionsof the envelope, or from only a single relatively small portion of thecircumference of the tube.

The advantage of a lamp in accordance with the invention is thatasymmetrical polar distribution of the emitted light is automaticallyobtained therefrom, by virtue of the shape of the envelope. This featureis particularly advantageous for street light and similar space lightingapplications, since asymmetrical light distribution in requireddirections can be obtained when the lamp is mounted in a fittingprovided with minimal op' tical arrangements,

In an arrangement comprising, in combination, a fit ting and a lamp inaccordance with the invention mounted therein, with the longitudinalaxes of both the lamp and the fitting lying horizontally, as is usual instreet lighting and similar installations, the lamp is preferably soarranged that those portions of the envelope wall from which the maximumemission of light is obtained in operation are disposed vertically, Thuswhere a trough-shaped fitting is employed, the said portions of theenvelope wall will be disposed substantially parallel to the sides ofthe fitting, which may be provided with suitable optical means, such asreflectors or diffractors, for deflecting the light emitted through thesaid portions of the envelope wall into desired down ward directions.Such an arrangement gives improved efficiency of utilisation of thelight emitted by the lamp, with the provision of only quite simpleoptical equipment in the fitting.

The discharge envelope may be closed at both ends by pinches (in thecase ofa fused silica envelope) or by suitably shaped refractory metalclosure members, in known manner. Niobium closure members are pre ferredfor use with a polycrystalline or crystalline alumina envelope, sincethe thermal expansion characteristics of niobium substantially matchthose of alumina; moreover niobium is especially suitable for use in ahigh pressure sodium lamp, since it is resistant to attack by hot sodiumvapour. Each metal closure member carries an electrode extendingcoaxially into the envelope and an external member for connection of theelectrode to a source of electric current supply for operation of thelamp, one of these external members usually being an exhaust tube foruse in evacuating the envelope and introducing the filling inmanufacture of the lamp. The metal closure members may be in the form ofdiscs, caps, or flanged recessed caps of the kind described in US, Pat.Specification No. 3,428,846, and may be sealed to the ends of an aluminatube in known manner, by means of a sealing glass or active alloy ofsuitable composition.

A lamp in accordance with the invention is mounted coaxially within acylindrical glass outer jacket designed to maintain the dischargeenvelope at a suitable high temperature when the lamp is in operation,in conventional manner.

Some specific embodiments of the invention will now be described by wayof example with reference to the accompanying drawings, in which FIG. Ishows, in part-sectional elevation, a lamp in accordance with theinvention having a discharge enve lope of elliptical cross-section,

FIG. 2 is a section drawn on the line Il-ll of FIG. I, and

FIGS. 3 to 17 show, in cross-section, various alternative configurationsof discharge envelopes for lamps in accordance with the invention.

The lamp shown in FIG. I is a high pressure sodium vapour discharge lampcomprising an envelope 1 formed of transparent crystalline corundumtubing of elliptical cross-section and uniform wall thickness, as shownby the transverse section constituting FIG. 2. The envelope is closed byniobium sheet end caps 2, 3,

which are sealed to the ends of the corundum tube by means of azirconium-titamum-vanadium alloy; the cap 2 carries an electrode 4 and aconnection tag 6. brazed to the interior and exterior surfacesrespectively of the cap, and a second electrode is supported by anexhaust tube 7, which is inserted through an aperture in the cap 3 andis brazed to the exterior of the cap. The electrodes are silicatedtungsten rods carrying on their inner ends small quantities of electronemissive material retained by coils of tungsten wire; and the tag 6 andexhaust tube 7 are of niobium; all brazes are effected with titanium.

In a specific example of a lamp of the form shown in FIGS. 1 and 2, thetubular envelope 1 is 100 mm long and has a uniform wall thickness of0.8 mm, and the internal cross-section of the tube has a major axis of 7mm and a minor axis of 5 mm, in length. The electrodes are l mm indiameter and 12 mm long, the part of the exhaust tube 7 extending withinthe envelope constituting part of the length of the electrode 5. Thelamp has a filling of sodium, mercury, and xenon at a pressure of 30Torr at room temperature.

The lamp envelopes shown in cross-section in FIGS. 3 and 4 also havewalls, 8 and 9 respectively, of uniform thickness, the envelope of FIG.3 being of ovate section and that of FIG. 4 of rectangular section.FIGS. 5, 6 and 7 show envelopes of generally rectangular section, withoptical elements built into the two longer sides of the wall in eachcase: thus in FIG. 5 the longer sides 10, ll of the rectangle areIenticular, in FIG. 6 they are in the form of prisms 12, 13, and in FIG.7 each of the longer sides is formed with multiple prisms 14, 15 on theexterior. In the case of the envelope shown in FIG. 8 the bore is ofsquare cross-section, and the exterior is of elliptical cross-section,so that the wall is formed with two relatively thick lenses 16, 17 ontwo opposite sides of the square bore, the other two sides 18, 19 of thewall also being lenticular but thinner.

The envelopes shown in FIGS. 9, 10, 11 and 12 all have circularcylindrical bores with variously shaped exteriors so that opticalelements are formed in the walls. Thus in FIG. 9 the exterior of theenvelope is of elliptical section and in FIG. 10 it is of substantiallyrectangular section, so that in each of these cases the wallincorporates a pair of thick lenses, 20, 21 and 22, 23 respectively, intwo opposite regions. The envelopes of FIGS. 11 and 12 have exteriorsrespectively of gen erally elliptical and generally rectangular section,but with multiple prisms 24, 25 and 26, 27 respectively formed on theexteriors of two opposite sides. In FIGS. 11 and 12 the multiple prismsare shown on the two shorter sides of the ellipse and the rectanglerespectively, but it will be appreciated that they could alternativelybe formed on the longer sides, the shorter sides then being lenticular.

The envelopes of FIGS. 13 and 14 both have bores of ellipticalcross-section; in the case of FIG. 13 the exterior of the envelope is ofcircular section, so that the wall incorporates lenses 28, 29, and inthe case of FIG. 14 the exterior is of generally circular section withmul tiple prisms 30, 31 formed in two opposite regions of the wall.

FIGS. 15, 16 and 17 all show envelopes with multiple prisms formed onthe internal surface of the wall. The envelope of FIG. is of ellipticalsection, with internal multiple prisms 32, 33 formed in the longer sidesof the wall; the envelope of FIG. 16 is of rectangular section withinternal multiple prisms 34, 35 formed in the longer sides of the wall;and the envelope of FIG. 17 is of circular section with internalmultiple prisms 36, 37 formed in two opposite regions of the Wall.

We claim:

1. A high pressure electric discharge lamp comprising a tubulardischarge envelope formed of transparent crystalline corundum, with apair of electrodes disposed coaxially within said envelope and carriedrespectively by closure means closing each end of the en velope, whereinat least one of the interior and exterior longitudinal surfaces of thetubular discharge envelope wall is of nonuniform conformation around thecircumference such that in any cross-section of the envelope thedistance of said surface from the longitudinal axis of the envelope isless in at least one region of the cross section than in the remainderof the cross-section, the cross-sectional conformation of the envelopewall being uniform throughout the length of the envelope, whereby thepolar distribution of light emitted from the lamp as a whole, inoperation of the lamp, is nonuniform around the circumference of th.envelope.

2. A lamp according to claim 1 wherein the interior and exteriorsurfaces of the envelope wall are of paral lel conformation, so that thewall thickness is uniform and both the exterior and interior of theenvelope are of similar cross-sectional conformation.

3. A lamp according to claim 2 wherein the cross section of the envelopehas one of the shapes consisting of an ellipse, an ovoid, andsubstantially a rectangle, whereby the maximum emission of light fromthe lamp in operation is obtained from two opposite regions in saidcross-section.

4. A lamp according to claim I wherein the interior and exteriorsurfaces of the envelope are of different conformation, so that in thecross-section of the envelope the wall is ofvarying thickness and atleast one optical element is incorporated in the wall structure.

5. A lamp according to claim 4 wherein at least one lens is incorporatedin the envelope wall structure.

6. A lamp according to claim 5 wherein a lens is incorporated in each oftwo opposite sides of the envelope wall, whereby the maximum emission oflight from the lamp in operation is obtained from the two oppositeregions in the cross-section of the envelope which comprise said lenses.

7. A lamp according to claim 4 wherein at least one prism isincorporated in the envelope wall structure.

8. A lamp according to claim 7 wherein a prism is incorporated in eachof two opposite sides of the envelope wall, whereby the maximum emissionof light from the lamp in operation is obtained from the two oppositeregions in the cross-section of the envelope which comprise said prisms.

9. A lamp according to claim 4 wherein at least one multiple prism isincorporated in the envelope wall structure.

10. A lamp according to claim 9 wherein a multiple prism is incorporatedin each of two opposite sides of the envelope wall, whereby the maximumemission of light from the lamp in operation is obtained from the twoopposite regions in the cross-section of the enve lope which comprisesaid multiple prisms.

1. A high pressure electric discharge lamp comprising a tubulardischarge envelope formed of transparent crystalline corundum, with apair of electrodes disposed coaxially within said envelope and carriedrespectively by closure means closing each end of the envelope, whereinat least one of the interior and exterior longitudinal surfaces of thetubular discharge envelope wall is of nonuniform conformation around thecircumference such that in any cross-section of the envelope thedistance of said surface from the longitudinal axis of the envelope isless in at least one region of the cross-section than in the remainderof the cross-section, the cross-sectional conformation of the envelopewall being uniform throughout the length of the envelope, whereby thepolar distribution of light emitted from the lamp as a whole, inoperation of the lamp, is non-uniform around the circumference of theenvelope.
 2. A lamp according to claim 1 wherein the interior andexterior surfaces of the envelope wall are of parallel conformation, sothat the wall thickness is uniform and both the exterior and interior ofthe envelope are of similar cross-sectional conformation.
 3. A lampaccording to claim 2 wherein the cross-section of the envelope has oneof the shapes consisting of an ellipse, an ovoid, and substantially arectangle, whereby the maximum emission of light from the lamp inoperation is obtained from two opposite regions in said cross-section.4. A lamp according to claim 1 wherein the interior and exteriorsurfaces of the envelope are of different conformation, so that in thecross-section of the envelope the wall is of varying thickness and atleast one optical element is incorporated in the wall structure.
 5. Alamp according to claim 4 wherein at least one lens is incorporated inthe envelope wall structure.
 6. A lamp according to claim 5 wherein alens is incorporated in each of two opposite sides of the envelope wall,whereby the maximum emission of light from the lamp in operation isobtained from the two opposite regions in the cross-section of theenvelope which comprise said lenses.
 7. A lamp according to claim 4wherein at least one prism is incorporated in the envelope wallstructure.
 8. A lamp according to claim 7 wherein a prism isincorporated in each of two opposite sides of the envelope wall, wherebythe maximum emission of light from the lamp in operation is obtainedfrom the two opposite regions in the cross-section of the envelope whichcomprise said prisms.
 9. A lamp according to claim 4 wherein at leastone multiple prism is incorporated in the envelope wall structure.
 10. Alamp according to claim 9 wherein a multiple prism is incorporated ineach of two opposite sides of the envelope wall, whereby the maximumemission of light from the lamp in operation is obtained from the twoopposite regions in the cross-section of the envelope which comprisesaid multiple prisms.